Magnetic flowmeter systems include a flowtube assembly and a transmitter assembly that are electrically connected to one another by one or more cables. The flowtube assembly receives an electric current from the transmitter assembly. The electric current produces a magnetic field in an insulated bore of the flowtube assembly. A liquid flows through the magnetic field in the insulated bore. The motion of the liquid in the magnetic field produces a flow voltage. According to Faraday's law of electromagnetic induction, the flow voltage is proportional to the velocity of flow. Electrodes in the insulated bore contact the flow voltage and the flow voltage is coupled by a cable to the transmitter assembly. The transmitter assembly measures the voltage and provides one or more scaled electrical outputs that represent the rate of flow of the liquid.
The flow voltage is a function of the shape of the magnetic field in the insulating bore, the current amplitude, the electrode spacing, the velocity of the fluid flow between the electrodes and other flowtube assembly design factors. The velocity of the fluid flow is a function of the volumetric flow rate of the fluid and the diameter of the insulated bore near the electrodes. The performance of the flowtube assembly can be approximated by Equations 1 and 2:K=E/(IQ)  Equation 1Q=V1(π)(D1/2)2=V2(π)(D2/2)2  Equation 2where E is the flow voltage, I is the electric current, Q is the volumetric flow rate, and K is a constant that represents the performance of the flowtube assembly. V1, D1 are the flow velocity and bore diameter near the electrodes. V2, D2 are the flow velocity and bore diameter in adjacent piping to which the flowtube assembly is coupled. The constant K takes into account all of the effects of electrode spacing, magnetic field shape, velocity as a function of volumetric flow rate and other design factors.
During manufacture or service of the flowtube assembly, the flowtube assembly is temporarily connected to a calibration system (meter prover, flow stand, flow laboratory, etc.). The calibration system provides a calibrated electric current and a calibrated volumetric flow rate. The calibration system measures the flow voltage. The constant K is calculated from the known values of current and volumetric flow rate and the measured value of flow voltage. The calculated constant K is recorded and serves as calibration data for the flowtube assembly. Typically, a manufacturer's calibration data is recorded on a nameplate of the flowtube assembly in a form that is peculiar to a particular manufacturer.
Different manufacturers use different systems of units in the data recorded on the flowtube assembly nameplate. In some cases, the data recorded on the nameplate is referenced indirectly to flow velocity at an assumed nominal pipe diameter rather than being referenced directly to volumetric flow rate. In some cases, the nameplate data can be subject to an assumed level of electric current provided the manufacturer's transmitter and represents (KI) instead of K. The complexity of the problem is compounded by the fact that transmitters are typically designed to operate with a range of many different diameters of flowtubes, and these diameters may, or may not be integrated into the nameplate data. The problem is further compounded by the fact that the nameplate data may, or may not, have a scale factor included in the same number that represents the constant K.
Different manufacturers design magnetic transmitter assemblies to accept a data entry of nameplate data that is taken from the manufacturer's own flowtube assemblies. There is usually no provision to enter nameplate data from flowtube assemblies made by another manufacturer.
The risks, complexity and transaction costs of converting one manufacturers nameplate data to the format of another manufacturer are so high that industrial users generally will not attempt to use a mixed flowmeter system that includes a flowtube assembly from one manufacturer with a transmitter assembly from another manufacturer. Most industrial users also do not have on-site access to flow calibration systems that could be used with mixed flowmeter systems to perform flow calibration that could bypass use of the nameplate data.
A method and apparatus are needed that will permit a user to utilize a mixed flowmeter system without the complexity of learning multiple manufacturers nameplate data system and computing a conversion from one nameplate data system to a different nameplate data system.